Illustrate the usage of the multiproc TSelector interfaces with the h1 analysis example.

Author: Anda Chelba, Gerardo Ganis
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Sunday, October 02, 2022 at 09:33 AM.

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%%cpp -d

#include "TString.h"
#include "TROOT.h"
#include "TChain.h"
#include "TBranch.h"
#include "TFileCollection.h"
#include "TH1F.h"
#include "TTreeReader.h"
#include "ROOT/TTreeProcessorMP.hxx"

#include <memory>

const auto file0 = "";
const std::vector<std::string> files = {file0,

MacOSX may generate connection to WindowServer errors

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TString selectorPath = gROOT->GetTutorialDir();
selectorPath += "/tree/h1analysis.C+";
std::cout << "selector used is: " << selectorPath << "\n";
auto sel = TSelector::GetSelector(selectorPath);

The following code generates a crash when Davix is used for HTTP Davix does not seem fork-safe; the problem has been reported to the Davix developers. For the time being we disable this part. To repoduce the problem, uncomment the next line.

define __reproduce_davix

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#if defined(__reproduce_davix)
auto fp = std::make_unique<TTree>(TFile::Open(file0));
auto tree = fp->Get<TTree>("h42");

ROOT::TTreeProcessorMP pool(3);

TList *out = nullptr;
#if defined(__reproduce_davix)

TTreeProcessorMP::Process with a single tree

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out = pool.Process(*tree, *sel);

TTreeProcessorMP::Process with single file name and tree name Note: we have less files than workers here

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out = pool.Process(file0, *sel, "h42");

Prepare datasets: vector of files, TFileCollection

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TChain ch;
TFileCollection fc;
for (auto &&file : files) {
   fc.Add(new TFileInfo(file.c_str()));

TTreeProcessorMP::Process with vector of files and tree name Note: we have more files than workers here (different behaviour)

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out = pool.Process(files, *sel, "h42");

TTreeProcessorMP::Process with TFileCollection, no tree name

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out = pool.Process(fc, *sel);

TTreeProcessorMP::Process with TChain, no tree name

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out = pool.Process(ch, *sel);

return 0;